Apparatus for monitoring the condition of a machine

ABSTRACT

A method for analyzing the condition of a machine, and an apparatus for analyzing the condition of a machine are described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 1200552-6,filed in the Kingdom of Sweden on Sep. 11, 2012, which is expresslyincorporated herein in its entirety by reference thereto.

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/732,483, filed on Dec. 3, 2012, which is expresslyincorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to a method for analysing the condition ofa machine, and to an apparatus for analysing the condition of a machine.The invention also relates to a system including such an apparatus andto a method of operating such an apparatus. The invention also relatesto a computer program for causing a computer to perform an analysisfunction.

DESCRIPTION OF RELATED ART

Machines with moving parts are subject to wear with the passage of time,which often causes the condition of the machine to deteriorate. Examplesof such machines with movable parts are motors, pumps, generators,compressors, lathes and CNC-machines. The movable parts may comprise ashaft and bearings.

In order to prevent machine failure, such machines should be subject tomaintenance, depending on the condition of the machine. Therefore theoperating condition of such a machine is preferably evaluated from timeto time. The operating condition can be determined by measuringvibrations emanating from a bearing or by measuring temperature on thecasing of the machine, which temperatures are dependent on the operatingcondition of the bearing. Such condition checks of machines withrotating or other moving parts are of great significance for safety andalso for the length of the life of such machines. It is known tomanually perform such measurements on machines. This ordinarily is doneby an operator with the help of a measuring instrument performingmeasurements at measuring points on one or several machines.

A number of commercial instruments are available, which rely on the factthat defects in rolling-element bearings generate short pulses, usuallycalled shock pulses. A shock pulse measuring apparatus may generateinformation indicative of the condition of a bearing or a machine.

WO 03062766 discloses a machine having a measuring point and a shaftwith a certain shaft diameter, wherein the shaft can rotate when themachine is in use. WO 03062766 also discloses an apparatus for analysingthe condition of a machine having a rotating shaft. The disclosedapparatus has a sensor for producing a measured value indicatingvibration at a measuring point. The apparatus disclosed in WO 03062766has a data processor and a memory. The memory may store program codewhich, when run on the data processor, will cause the analysis apparatusto perform a Machine Condition Monitoring function. Such a MachineCondition Monitoring function may include shock pulse measuring.

SUMMARY

An aspect of the invention relates to the problem of providing animproved method and an improved apparatus for analysis of the conditionof a machine having a rotating part.

This problem is addressed by an apparatus for analysing the condition ofa machine as described below. Various embodiments are disclosed below:An embodiment 1 comprises an apparatus for analysing the condition of amachine having a part (7,8) rotatable with a speed of rotation(f_(ROT)), comprising:

-   -   a transducer (10) for generating an analogue measurement signal        (SEA) in response to machine vibration so that said analogue        measurement signal (SEA) includes a vibration signal signature        (SD) having        -   a vibration frequency (f_(SEA)) which is lower than an upper            frequency limit value (f_(SEAmax)) and        -   at least one vibration signal repetition frequency (f_(D))            and        -   a vibration signal amplitude;    -   an A/D converter (40, 44) adapted to generate a digital        measurement signal (S_(MD), S_(R)) having a sequence of sample        values (S_(MD), S_(R)) dependent on the analogue measurement        signal (S_(EA)), said digital measurement signal (S_(MD), S_(R))        having a first sample rate (f_(s));    -   a digital peak value detector (310) adapted to generate output        peak values (A_(PO)) dependent on said sequence of sample values        (S_(MD), S_(R));    -   a peak value discriminator (870) being adapted to sort said        output peak values (A_(PO)) into corresponding amplitude ranges        during a measuring session;    -   a measuring session controller (904) adapted to control a        duration (T_(Meas)) of said measuring session;    -   a condition value generator (1030) adapted to generate a first        condition value (LR_(D)) in response to said sorted output peak        values (A_(PO)) and said duration (T_(Meas)) so that        -   said first condition value (LR_(D)) is indicative of a first            amplitude value (A_(LRD)) having a first predetermined            occurrence rate (f_(C1)), and so that        -   said first condition value (LR_(D)) is based on a selected            first temporal portion of the digital measurement signal            (S_(MD), S_(R)); the apparatus further comprising    -   a decimator (1010) adapted to generate a decimated digital        signal (S_(RED); S_(RED1); S_(RED2)) in dependence of said        digital measurement signal (S_(MD), S_(R)) so that the decimated        digital signal (S_(RED); S_(RED1); S_(RED2)) has a reduced        sampling frequency (f_(SR1); f_(SR1)); and    -   a Fourier Transformer (1020) adapted to generate a transformed        signal (S_(FT)) in dependence of a selected second temporal        portion of said decimated digital signal (S_(RED); S_(RED1);        S_(RED2)) so that said transformed signal (SFT) is indicative of        said vibration signal repetition frequency (f_(D)); said        apparatus being arranged to        -   coordinate the generation of said transformed signal (SFT)            with the generation of the first condition value (LR_(D)) so            that            -   the selected second temporal portion of said decimated                digital signal (S_(RED); S_(RED1); S_(RED2)) is based                substantially on said selected first temporal portion of                the digital measurement signal (S_(MD)), and so that                said selected first temporal portion of the digital                measurement signal (S_(MD)) is generated during the                duration (T_(Meas)) of said measuring session.

This solution advantageously enables the delivery of

-   -   a first condition value (LR_(D)) which is indicative of the        first amplitude value (A_(LRD)) of peak values (A_(PO)) having a        first predetermined occurrence rate (f_(C1)) and of        -   a transformed signal (SFT) which is indicative of said            vibration signal repetition frequency (f_(D)) while ensuring            that the first condition value (LR_(D)) and the transformed            signal (SFT) are consistent with each other, since both of            them are based on the same or substantially the same            temporal portion of the digital measurement signal (S_(MD)).

Hence, the first condition value (LR_(D)) and the transformed signal(SFT) are based on concurrent measurement data, or substantially thesame measurement data, and as such the first condition value (LR_(D))and the transformed signal (SFT) may complement each other by providingmutually different perspectives on the same event, i.e. the condition ofthe monitored rotatable machine part (7,8) during the measuring session,based on data collected during the whole duration (T_(meas)) of themeasuring session. According to a preferred embodiment said first samplerate (f_(s)) is at least twice said upper frequency limit value(f_(SEAmax)). According to a most preferred embodiment the duration(T_(Meas)) of said measuring session is a variably settable duration(T_(Meas)).

Embodiment 2: The apparatus according to claim 1, wherein

-   -   the condition value generator (1030) is adapted to generate a        second condition value (HR_(LUB)) in response to said sorted        output peak values (A_(PO)) and said duration (T_(Meas)) so that    -   said second condition value (HR_(LUB)) is indicative of a second        amplitude value (A_(HRLUB)) having a second predetermined        occurrence rate (f_(C2)), and so that    -   said second condition value (HR_(LUB)) is based on said selected        first temporal portion of the digital measurement signal        (S_(MD), S_(R)).

According to an embodiment, the first condition value (LR_(D)) isindicative of the amplitude (A_(LRD)) of peak values (A_(PO)) having afirst predetermined occurrence rate f_(C1) of e.g. f_(C1)=40 pulses persecond, and the second condition value (HR_(LUB)) is indicative of asecond amplitude value (A_(HRLUB)) having a second predeterminedoccurrence rate f_(C2) of e.g. f_(C2)=1000 pulses per second.

Measurement experience indicates that, during operation of a specificundamaged rotational part, such as a roller bearing, the amplitudelevels of the first condition value (LR_(D)) and the second conditionvalue (HR_(LUB)) vary with the amount of lubrication in between therolling elements and the raceway, whereas a relation between firstcondition value (LR_(D)) and the second condition value (HR_(LUB))remains substantially constant. However, when a surface damage occurs inthe rotational part, e.g. in the raceway, measurement experienceindicate that the amplitude values of the first condition value (LR_(D))as well the second condition value (HR_(LUB)) increase significantly,and there is also a distinguishable change in the relation between firstcondition value (LR_(D)) and the second condition value (HR_(LUB)). Moreparticularly, although both of the condition values (LR_(D) andHR_(LUB)) increase in response to a surface damage, the amplitude offirst condition value (LR_(D)) increases distinctly more than theamplitude of the second condition value (HR_(LUB)).

Accordingly, the combination of the values of the first condition value(LR_(D)) and the second condition value (HR_(LUB)) may be interpreted toindicate not only a lubrication condition of the rotational part, but itis also indicative of the mechanical condition of the surfaces of therotational part.

Advantageously, this solution enables the delivery of a transformedsignal (SFT) which is indicative of said vibration signal repetitionfrequency (f_(D)) while ensuring that the first condition value(LR_(D)), the second condition value (HR_(LUB)) and the transformedsignal (SFT) are consistent with each other, since all these data arebased on the same or substantially the same temporal portion of thedigital measurement signal (S_(MD)). The first and the second conditionvalues (LR_(D), HR_(LUB)) are consistent with the transformed signal(SFT) in that they provide mutually different aspects of the conditionof the monitored rotational part. So, for example, when damage occurs inthe raceway of a monitored bearing, the first and the second conditionvalues (LR_(D), HR_(LUB)) will increase, as described above, thusindicating the presence of a surface damage. When the first and thesecond condition values (LR_(D), HR_(LUB)) increase to such an extent asto indicate the presence of an incipient damage to the monitoredrotational part, experience has shown that the transformed signal willprovide information about what type of damage there is. Hence, the firstand the second condition values (LR_(D), HR_(LUB)) as well as thetransformed signal (SFT) are based on concurrent measurement data, orsubstantially the same measurement data, and as such the first and thesecond condition values (LR_(D), HR_(LUB)) and the transformed signal(SFT) complement each other by providing mutually different perspectiveson the same event, i.e. the condition of the monitored rotatable machinepart (7,8) during the measuring session, based on data collected duringthe whole duration of the measuring session.

Since the transformed signal (SFT) is indicative of the vibration signalrepetition frequency (f_(D)), it may be possible to establish e.g.whether the incipient damage is located on the inner ring of themonitored bearing or on the outer ring of the monitored bearing.

Embodiment 3: The apparatus according to embodiment 1 or 2, furthercomprising

-   -   an analyser (290) having        -   a first analyzer input 1050 for receiving said first            condition value (LR_(D));        -   a second analyzer input 1060 for receiving said second            condition value (HR_(LUB)); wherein    -   the analyzer is adapted to generate a status signal indicative        of whether the condition of the machine is normal or abnormal in        dependence on said first condition value (LR_(D)) and said        second condition value (HR_(LUB)).

The fact that the apparatus may generate the first condition value(LR_(D)) and the second condition value (HR_(LUB)) on the basis ofmeasurement data (S_(MD), S_(R)) collected during the uninterrupted timeperiod of the variably settable duration (T_(Meas)) of said measuringsession advantageously increases the reliability of the first conditionvalue (LR_(D)) and the second condition value (HR_(LUB)) in the sense oftruly reflecting the condition of the monitored part. When, for example,the monitored rotatable part is a bearing in a crane which sometimescarries a heavy load, and which sometimes runs substantially unloaded,the bearing will sometimes be subjected to a large force due to thecarrying of the heavy load. In such a case it is desirable that themeasurement data collected, i.e. the selected first temporal portion ofthe digital measurement signal (S_(MD), S_(R)), includes the time periodwhen the bearing is subjected to a large force. The variably settableduration (T_(Meas)) of the measurement session advantageously enables anoperator of the apparatus to set the duration (T_(Meas)) so as toinclude the loaded time period in the measurement session.

Embodiment 4: The apparatus according to embodiment 3, furthercomprising

-   -   an apparatus input for receiving a signal indicative of a        detected speed of rotation (f_(ROT)) associated with said        rotatable part (7,8);        -   a third analyzer input 1070 for receiving said signal            indicative of a detected speed of rotation (f_(ROT));        -   a fourth analyzer input 1080 for receiving a bearing            frequency factor value (OR, IR, FTF, BS); and        -   a fifth analyzer input 1090 for receiving said transformed            signal (S_(FT), f_(D)); wherein    -   the analyzer is adapted to generate a status signal indicative        of the nature of, and/or cause for, an abnormal machine        condition in dependence of said speed of rotation signal        (f_(ROT)), said bearing frequency factor value (OR, IR, FTF, BS)        and said transformed signal (S_(FT), f_(D)).

Embodiment 5: The apparatus according to embodiment 3, furthercomprising

-   -   an apparatus input for receiving a signal indicative of a        detected speed of rotation (f_(ROT)) associated with said        rotatable part (7,8);        -   a third analyzer 1070 input for receiving said signal            indicative of a detected speed of rotation (f_(ROT));        -   a fourth analyzer input 1080 for receiving a bearing            frequency factor value (OR, IR, FTF, BS); and        -   a fifth analyzer input 1090 for receiving said transformed            signal (S_(FT), f_(D));    -   wherein    -   the analyzer is adapted to generate a status signal indicative        of a probable location of an incipient damage in dependence of        -   said speed of rotation signal (f_(ROT)),        -   said bearing frequency factor value (OR, IR, FTF, BS) and        -   said transformed signal (S_(FT), f_(D)).

Embodiment 6: The apparatus according to embodiment 3, furthercomprising

-   -   an apparatus input 1040 for receiving a signal indicative of a        detected speed of rotation (f_(ROT)) associated with said        rotatable part (7,8);        -   a third analyzer input 1070 for receiving said signal            indicative of a detected speed of rotation (f_(ROT));        -   a fourth analyzer input 1080 for receiving a bearing            frequency factor value (OR, IR, FTF, BS); and        -   a fifth analyzer input 1090 for receiving said transformed            signal (S_(FT), f_(D));    -   wherein    -   the analyzer is adapted to extract said at least one vibration        signal repetition frequency (f_(D)) from said transformed signal        (S_(FT), f_(D)); and        -   the analyzer is adapted to generate a frequency factor            estimate (F_(fEST)) in dependence on said at least one            vibration signal repetition frequency (f_(D)) and said            detected speed of rotation (f_(ROT)); and        -   the analyzer is adapted to compare the generated frequency            factor estimate (F_(fEST)) with a stored plurality of            frequency factors (F_(fstore1), F_(fstore2), F_(fstore3), .            . . F_(fstoren)); and wherein        -   the analyzer is adapted to generate a status signal            indicative of a probable location of an incipient damage in            dependence of said frequency factor comparison.

This solution may advantageously provide an explicit indication to theeffect that a detected damage is located e.g. on the outer ring of amonitored bearing assembly, when the generated frequency factor estimate(F_(fEST)) has a value that substantially corresponds to a stored valueof an Outer Ring frequency factor value.

Embodiment 7: The apparatus according to any of embodiments 1 to 6,further comprising:

-   -   an associator (1035, 290) adapted to associate        -   said first condition value (LR_(D)) with        -   said transformed signal (SFT).

Embodiment 8: The apparatus according to any of embodiments 1 to 6,further comprising:

-   -   a digital rectifier (270 adapted to perform a rectification so        as to generate a rectified digital signal (SR) dependent on said        digital measurement signal (SMD); and wherein    -   the digital peak value detector (310) is adapted to generate the        output peak values (APO) dependent on said rectified digital        signal (SMD, SR); and    -   said decimator (1010) is adapted to perform said decimation on        the rectified digital signal (SR) so as to achieve said        decimated digital signal (SRED; SRED1; SRED2) having a reduced        sampling frequency (fSR; fSR1).

Embodiment 9: The apparatus according to embodiment 8, wherein:

-   -   the digital rectifier (270) is adapted to perform a full-wave        rectification so as to generate a rectified digital signal (SR)        dependent on said digital measurement signal (SMD) including        absolute values of said sequence of sample values (S_(MD),        S_(R)).

Embodiment 10: An apparatus for analysing the condition of a machinehaving a part (7) rotatable with a speed of rotation (f_(ROT)),comprising

-   -   an input (42) for receiving an analogue measurement signal        (S_(EA)) indicative of a vibration signal signature (S_(D))        having a vibration frequency (f_(SEA)) and at least one        repetition frequency (f_(D));    -   an A/D converter (40, 44) adapted to generate a digital        measurement signal (S_(MD)) having a sequence of sample values        dependent on the analogue measurement signal, said digital        measurement signal (S_(MD)) having a first sample rate (fS),        wherein said vibration frequency (fSEA) is assumed to be lower        than half of the first sample rate (fS);    -   a digital rectifier (270) adapted to perform a rectification so        as to generate a rectified digital signal (SR) dependent on said        digital measurement signal (S_(MD));    -   a digital peak value detector (310) adapted to deliver output        peak values (APO) on a peak value detector output (315)        dependent on said rectified digital signal (S_(R));    -   a peak value discriminator (870) being adapted to sort said        output peak values (A_(PO)) into corresponding amplitude ranges        during a measuring session;    -   a measuring session controller (904) adapted to control a        duration (T_(Meas)) of said measuring session;    -   a condition value generator adapted to generate a first        condition value (LR_(D)) in response to said sorted output peak        values (A_(PO)) and said duration (T_(Meas)) so that said first        condition value (LR_(D)) is based on a selected first temporal        portion of the digital measurement signal (S_(MD)); the        apparatus further comprising    -   a decimator (1010) for performing a decimation of the rectified        digital signal (S_(R)) so as to achieve a decimated digital        signal (S_(RED); S_(RED1); S_(RED2)) having a reduced sampling        frequency (f_(SR); f_(SR1)); and    -   a Fourier Tranformer (1020) adapted to generate a transformed        signal (SFT) in dependence on a selected second temporal portion        of said decimated digital signal (S_(RED); S_(RED1); S_(RED2));        said apparatus being arranged to        -   coordinate the generation of said transformed signal (SFT)            with the generation of the first condition value (LR_(D)) so            that the selected second temporal portion of said decimated            digital signal (S_(RED); S_(RED1); S_(RED2)) is based            substantially on said selected first temporal portion of the            digital measurement signal (S_(MD)).

Problem: Correct detection of peak values in an analogue measurementsignal (S_(EA)) having transient vibration signal signatures (S_(D))having a vibration frequency (f_(SEA)) and at least one repetitionfrequency (f_(D)) require a high sample rate in order to actually samplethe analogue signal at a moment of peak value. This problem is addressedby the following embodiment:

Embodiment 11: An apparatus for analysing the condition of a machinehaving a part (7) rotatable with a speed of rotation (f_(ROT)),comprising

an input (42) for receiving an analogue measurement signal (S_(EA))indicative of a vibration signal signature (S_(D)) having a vibrationfrequency (f_(SEA)) and at least one repetition frequency (f_(D));

an A/D converter (40, 44) adapted to generate a digital measurementsignal (S_(MD)) dependent on the analogue measurement signal, saiddigital measurement signal (S_(MD)) having a first sample rate (f_(s)),the first sample rate being at least twice (k) said vibration frequency(f_(SEA));

a digital rectifier (270) adapted to perform full-wave rectification soas to generate a rectified digital signal (S_(R)) dependent on saiddigital measurement signal (S_(MD));

-   -   a smoothing stage (TOP-3) adapted to generate a smoothened        digital signal (S_(smooth)) dependent on said rectified digital        signal (S_(R)); said smoothing stage (TOP-3) being adapted to        adjust an output sample amplitude value (S_(SOUT) _(_) _(i))        upwards in dependence on        -   the amplitude of the corresponding input sample amplitude            value (S_(SIN) _(_) _(i)) and in dependence on        -   the amplitude of temporally adjacent input sample amplitude            values (S_(SIN) _(_) _(i−1), S_(SIN) _(_) _(i+1));    -   an asymmetric digital filter for generating an asymmetrically        low pass filtered signal (S_(ASYM)) in response to the smoothed        digital signal (S_(smooth)); the asymmetric digital filter being        adapted to generate the asymmetrically filtered signal        (S_(ASYM)) so that        -   in response to a detected positive time derivative of the            smoothed digital signal a first settable filter value (k) is            set to a first value (KRise); and        -   in response to a detected negative time derivative of the            smoothed digital signal said first settable filter value (k)            is set to a second value (kFall);    -   a peak value detector (330) adapted to deliver output peak        values (A_(PO)) on a peak value detector output (333) in        response to said detected peak values (A_(P)); and wherein    -   said peak value detector is adapted to limit the delivery        frequency of said output peak values (A_(P), A_(PO)) such that        said output peak values (A_(P), A_(PO)) are delivered at a        maximum delivery frequency of f_(dP), wherein

f _(dP) =f _(s) /e

-   -   -   where f_(s) is said first sample rate, and        -   e is an a number higher than two.

    -   Advantageously, the smoothing stage will eliminate “dents” in        the rectified signal, and it will do so by always adjusting the        amplitude upwards. Thus, whereas the rectified signal may        include a sampled value having significantly lower amplitude        that its neighbour samples, the signal from the smoothing stage        will always be smooth. Whereas such a smoothing effect may also        be achieved by means of a median-value-filter, the median-filter        would also reduce the top amplitude value of the output signal        in relation to the top value of the rectified input signal.        Hence, whereas a median-filter would make the signal more        smooth, the smoothing stage as defined above will not only make        the signal more smooth, but it will also maintain the amplitude        values of the highest detected amplitudes in the rectified        signal.

Embodiment 12: The apparatus according to embodiment 11, wherein

the smoothing stage includes

-   -   a first peak sample selector (TOP-3) adapted to analyze v        consecutive received sample values, and to identify the highest        amplitude of these v consecutive received sample values, and to        deliver v consecutive output sample values with at least one of        the v consecutive output sample values having an adjusted        amplitude value, said adjustment being an amplitude increase,    -   wherein, v is an integer having a value of about fs/f_(SEA).

Embodiment 13: The apparatus according to embodiment 11, wherein

the smoothing stage includes

a first peak sample selector which is adapted to receive a plurality oftemporally consecutive sample values; and

-   -   identify the amplitude of a selected sample value from among        said received plurality of consecutive sample values; and    -   analyze        -   the amplitude of the selected sample value,        -   the amplitude of the sample immediately preceding the            selected sample value and        -   the amplitude of the sample succeeding the selected sample            value; and    -   deliver an output sample value in response to said selected        sample value so that said output sample value has an amplitude        corresponding to the highest amplitude detected in said        analysis.

Embodiment 14: The apparatus according to embodiment 11, wherein:

-   -   the asymmetric digital filter is adapted to generate the        asymmetrically filtered signal (S_(ASYM)) so that        -   in response to a detected positive time derivative of the            smoothed digital signal (S_(smooth)) the asymmetrically            filtered signal (S_(ASYM)) will have a positive time            derivative substantially equal to that of the smoothed            digital signal (S_(smooth)); and        -   in response to a detected negative time derivative of the            smoothed digital signal (S_(smooth)) the asymmetrically            filtered signal (S_(ASYM)) will have a comparatively slow            response.

Embodiment 15: The apparatus according to any of embodiments 11-14,further comprising a decimator, a fourier transformer and a measuringsession controller as defined in embodiment 1.

Embodiment 16: The apparatus according to embodiment 15, wherein

-   -   said apparatus is arranged to coordinate the generation of said        transformed signal (SFT) with the generation of the first        condition value (LR_(D)) so that        -   the selected second temporal portion of said decimated            digital signal (S_(RED); S_(RED1); S_(RED2)) is based            substantially on said selected first temporal portion of the            digital measurement signal (S_(MD)), and so that said            selected first temporal portion of the digital measurement            signal (S_(MD)) is generated during the variably settable            duration (T_(Meas)) of said measuring session.

BRIEF DESCRIPTION OF THE DRAWINGS

For simple understanding of the present invention, it will be describedby means of examples and with reference to the accompanying drawings, ofwhich:

FIG. 1 shows a schematic block diagram of an embodiment of a conditionanalyzing system 2 according to an embodiment of the invention includingan analysis apparatus.

FIG. 2A is a schematic block diagram of an embodiment of a part of thecondition analyzing system 2 shown in FIG. 1 including an embodiment ofan analysis apparatus.

FIG. 2B is a schematic block diagram of an embodiment of a sensorinterface.

FIG. 2C is an illustration of a measuring signal from a vibrationsensor.

FIG. 2D illustrates a measuring signal amplitude generated by a shockpulse sensor.

FIG. 2E illustrates a measuring signal amplitude generated by avibration sensor. FIG. 3 is a simplified illustration of a Shock PulseMeasurement sensor according to an embodiment of the invention.

FIG. 4 is a simplified illustration of an embodiment of the memory 60and its contents.

FIG. 5 is a schematic block diagram of an embodiment of the analysisapparatus at a client location with a machine 6 having a movable shaft.

FIG. 6A illustrates a schematic block diagram of an embodiment of thepre-processor according to an embodiment of the present invention.

FIG. 6B illustrates an embodiment of the pre-processor including adigital rectifier.

FIG. 7 illustrates an embodiment of the evaluator.

FIG. 8 is a schematic block diagram of an embodiment of the analysisapparatus

FIG. 9 is a schematic illustration of plural memory positions arrangedas a table.

FIG. 10 illustrates a histogram having plural amplitude bins.

FIG. 11 is an illustration of a cumulative histogram table correspondingto the histogram table of FIG. 9.

FIG. 12 is a schematic block diagram of another embodiment of theanalysis apparatus.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following description similar features in different embodimentsmay be indicated by the same reference numerals.

FIG. 1 shows a schematic block diagram of an embodiment of a conditionanalyzing system 2 according to an embodiment of the invention.Reference numeral 4 relates to a client location with a machine 6 havinga movable part 8. The movable part may comprise bearings 7 and a shaft 8which, when the machine is in operation, rotates. The operatingcondition of the shaft 8 or of a bearing 7 can be determined in responseto vibrations emanating from the shaft and/or bearing when the shaftrotates. The client location 4, which may also be referred to as clientpart or user part, may for example be the premises of a wind farm, i.e.a group of wind turbines at a location, or the premises of a paper millplant, or some other manufacturing plant having machines with movableparts.

An embodiment of the condition analyzing system 2 is operative when asensor 10 is attached on or at a measuring point 12 on the body of themachine 6. Although FIG. 1 only illustrates two measuring points 12, itto be understood that a location 4 may comprise any number of measuringpoints 12. The condition analysis system 2 shown in FIG. 1, comprises ananalysis apparatus 14 for analysing the condition of a machine on thebasis of measurement values delivered by the sensor 10.

The analysis apparatus 14 has a communication port 16 for bi-directionaldata exchange. The communication port 16 is connectable to acommunications network 18, e.g. via a data interface 19. Thecommunications network 18 may be the world wide internet, also known asthe Internet. The communications network 18 may also comprise a publicswitched telephone network.

A server computer 20 is connected to the communications network 18. Theserver 20 may comprise a database 22, user input/output interfaces 24and data processing hardware 26, and a communications port 29. Theserver computer 20 is located on a location 28, which is geographicallyseparate from the client location 4. The server location 28 may be in afirst city, such as the Swedish capital Stockholm, and the clientlocation may be in another city, such as Stuttgart, Germany or Detroitin Michigan, USA. Alternatively, the server location 28 may be in afirst part of a town and the client location may be in another part ofthe same town. The server location 28 may also be referred to assupplier part 28, or supplier part location 28.

According to an embodiment of the invention a central control location31 comprises a control computer 33 having data processing hardware andsoftware for surveying a plurality of machines at the client location 4.The machines 6 may be wind turbines or gear boxes used in wind turbines.Alternatively the machines may include machinery in e.g. a paper mill.The control computer 33 may comprise a database 22B, user input/outputinterfaces 24B and data processing hardware 26B, and a communicationsport 29B. The central control location 31 may be separated from theclient location 4 by a geographic distance. By means of communicationsport 29B the control computer 33 can be coupled to communicate withanalysis apparatus 14 via port 16. The analysis apparatus 14 may delivermeasurement data being partly processed so as to allow further signalprocessing and/or analysis to be performed at the central location 31 bycontrol computer 33.

A supplier company occupies the supplier part location 28. The suppliercompany may sell and deliver analysis apparatuses 14 and/or software foruse in an analysis apparatus 14. The supplier company may also sell anddeliver analysis software for use in the control computer at the centralcontrol location 31. Such analysis software 94,105 is discussed inconnection with FIG. 4 below. Such analysis software 94,105 may bedelivered by transmission over said communications network 18.

According to one embodiment of the system 2 the apparatus 14 is aportable apparatus which may be connected to the communications network18 from time to time.

According to another embodiment of the system 2 the apparatus 14 isconnected to the communications network 18 substantially continuously.Hence, the apparatus 14 according to this embodiment may substantiallyalways be “on line” available for communication with the suppliercomputer 20 and/or with the control computer 33 at control location 31.

FIG. 2A is a schematic block diagram of an embodiment of a part of thecondition analyzing system 2 shown in FIG. 1. The condition analyzingsystem, as illustrated in FIG. 2A, comprises a sensor unit 10 forproducing a measured value. The measured value may be dependent onmovement or, more precisely, dependent on vibrations or shock pulsescaused by bearings when the shaft rotates.

An embodiment of the condition analyzing system 2 is operative when adevice 30 is firmly mounted on or at a measuring point on a machine 6.The device 30 mounted at the measuring point may be referred to as astud 30. A stud 30 can comprise a connection coupling 32 to which thesensor unit 10 is removably attachable. The connection coupling 32 can,for example comprise double start threads for enabling the sensor unitto be mechanically engaged with the stud by means of a ¼ turn rotation.

A measuring point 12 can comprise a threaded recess in the casing of themachine. A stud 30 may have a protruding part with threads correspondingto those of the recess for enabling the stud to be firmly attached tothe measuring point by introduction into the recess like a bolt.

Alternatively, a measuring point can comprise a threaded recess in thecasing of the machine, and the sensor unit 10 may comprise correspondingthreads so that it can be directly introduced into the recess.Alternatively, the measuring point is marked on the casing of themachine only with a painted mark.

The machine 6 exemplified in FIG. 2A may have a rotating shaft with acertain shaft diameter d1. The shaft in the machine 24 may rotate with aspeed of rotation V1 when the machine 6 is in use.

The sensor unit 10 may be coupled to the apparatus 14 for analysing thecondition of a machine. With reference to FIG. 2A, the analysisapparatus 14 comprises a sensor interface 40 for receiving a measuredsignal or measurement data, produced by the sensor 10. The sensorinterface 40 is coupled to a data processing means 50 capable ofcontrolling the operation of the analysis apparatus 14 in accordancewith program code. The data processing means 50 is also coupled to amemory 60 for storing said program code.

According to an embodiment of the invention the sensor interface 40comprises an input 42 for receiving an analogue signal, the input 42being connected to an analogue-to-digital (A/D) converter 44, thedigital output 48 of which is coupled to the data processing means 50.The A/D converter 44 samples the received analogue signal with a certainsampling frequency f_(s) so as to deliver a digital measurement datasignal S_(MD) having said certain sampling frequency f_(s) and whereinthe amplitude of each sample depends on the amplitude of the receivedanalogue signal at the moment of sampling.

According to another embodiment of the invention, illustrated in FIG.2B, the sensor interface 40 comprises an input 42 for receiving ananalogue signal S_(EA) from a Shock Pulse Measurement Sensor, aconditioning circuit 43 coupled to receive the analogue signal, and anA/D converter 44 coupled to receive the conditioned analogue signal fromthe conditioning circuit 43. The A/D converter 44 samples the receivedconditioned analogue signal with a certain sampling frequency f_(s) soas to deliver a digital measurement data signal S_(MD) having saidcertain sampling frequency f_(s) and wherein the amplitude of eachsample depends on the amplitude of the received analogue signal at themoment of sampling.

The sampling theorem guarantees that bandlimited signals (i.e., signalswhich have a maximum frequency) can be reconstructed perfectly fromtheir sampled version, if the sampling rate f_(s) is more than twice themaximum frequency f_(SEAmax) of the analogue signal S_(EA) to bemonitored. The frequency equal to one-half of the sampling rate istherefore a theoretical limit on the highest frequency that can beunambiguously represented by the sampled signal S_(MD). This frequency(half the sampling rate) is called the Nyquist frequency of the samplingsystem. Frequencies above the Nyquist frequency f_(N) can be observed inthe sampled signal, but their frequency is ambiguous. That is, afrequency component with frequency f cannot be distinguished from othercomponents with frequencies B*f_(N)+f, and B*f_(N)−f

for nonzero integers B. This ambiguity, known as aliasing may be handledby filtering the signal with an anti-aliasing filter (usually a low-passfilter with cutoff near the Nyquist frequency) before conversion to thesampled discrete representation.

In order to provide a safety margin for in terms of allowing a non-idealfilter to have a certain slope in the frequency response, the samplingfrequency may be selected to a higher value than 2. Hence, according toembodiments of the invention the sampling frequency may be set to

f _(s) =k*f _(SEAmax)

wherein

-   -   k is a factor having a value higher than 2.0

Accordingly the factor k may be selected to a value higher than 2.0.Preferably factor k may be selected to a value between 2.0 and 2.9 inorder to provide a good safety margin while avoiding to generateunnecessarily many sample values. According to an embodiment the factork is advantageously selected such that 100*k/2 renders an integer.According to an embodiment the factor k may be set to 2.56. Selecting kto 2.56 renders 100*k=256=2 raised to 8.

According to an embodiment the sampling frequency f_(s) of the digitalmeasurement data signal S_(MD) may be fixed to a certain value f_(s),such as e.g. f_(s)=102 kHz

Hence, when the sampling frequency f_(s) is fixed to a certain valuef_(s), the maximum frequency f_(SEAmax) of the analogue signal S_(EA)will be:

f _(SEAmax) =f _(s) /k

wherein f_(SEAmax) is the highest frequency to be analyzed in thesampled signal

Hence, when the sampling frequency f_(s) is fixed to a certain valuef_(s)=102 400 Hz, and the factor k is set to 2.56, the maximum frequencyf_(SEAmax) of the analogue signal S_(EA) will be:

f _(SEAmax) =f _(s) /k=102 400/2.56=40 kHz

Accordingly, a digital measurement data signal S_(MD), having a certainsampling frequency f_(s), is generated in response to said receivedanalogue measurement signal S_(EA). The digital output 48 of the A/Dconverter 44 is coupled to the data processing means 50 via an output 49of the sensor interface 40 so as to deliver the digital measurement datasignal S_(MD) to the data processing means 50.

The sensor unit 10 may comprise a vibration transducer, the sensor unitbeing structured to physically engage the connection coupling of themeasuring point so that vibrations of the machine at the measuring pointare transferred to the vibration transducer. According to an embodimentof the invention the sensor unit comprises a transducer having apiezo-electric element. When the measuring point 12 vibrates, the sensorunit 10, or at least a part of it, also vibrates and the transducer thenproduces an electrical signal of which the frequency and amplitudedepend on the mechanical vibration frequency and the vibration amplitudeof the measuring point 12, respectively. According to an embodiment ofthe invention the sensor unit 10 is a vibration sensor, providing ananalogue amplitude signal of e.g. 10 mV/g in the Frequency Range 1.00 to10000 Hz. Such a vibration sensor is designed to deliver substantiallythe same amplitude of 10 mV irrespective of whether it is exerted to theacceleration of 1 g (9.82 m/s²) at 1 Hz, 3 Hz or 10 Hz. Hence, a typicalvibration sensor has a linear response in a specified frequency range upto around 10 kHz. Mechanical vibrations in that frequency rangeemanating from rotating machine parts are usually caused by imbalance ormisalignment. However, when mounted on a machine the linear responsevibration sensor typically also has several different mechanicalresonance frequencies dependent on the physical path between sensor andvibration source.

A damage in a roller bearing may cause relatively sharp elastic waves,known as shock pulses, travelling along a physical path in the housingof a machine before reaching the sensor. Such shock pulses often have abroad frequency spectrum. The amplitude of a roller bearing shock pulseis typically lower than the amplitude of a vibration caused by imbalanceor misalignment.

The broad frequency spectrum of shock pulse signatures enables them toactivate a “ringing response” or a resonance at a resonance frequencyassociated with the sensor. Hence, a typical measuring signal from avibration sensor may have a wave form as shown in FIG. 2C, i.e. adominant low frequency signal with a superimposed higher frequency loweramplitude resonant “ringing response”.

In order to enable analysis of the shock pulse signature, oftenemanating from a bearing damage, the low frequency component must befiltered out. This can be achieved by means of a high pass filter or bymeans of a band pass filter. However, these filters must be adjustedsuch that the low frequency signal portion is blocked while the highfrequency signal portion is passed on. An individual vibration sensorwill typically have one resonance frequency associated with the physicalpath from one shock pulse signal source, and a different resonancefrequency associated with the physical path from another shock pulsesignal source, as mentioned in U.S. Pat. No. 6,053,047. Hence, filteradjustment aiming to pass the high frequency signal portion requiresindividual adaptation when a vibration sensor is used.

When such filter is correctly adjusted the resulting signal will consistof the shock pulse signature(s). However, the analysis of the shockpulse signature(s) emanating from a vibration sensor is somewhatimpaired by the fact that the amplitude response as well as resonancefrequency inherently varies dependent on the individual physical pathfrom the shock pulse signal sources.

Advantageously, these drawbacks associated with vibration sensors may bealleviated by the use of a Shock Pulse Measurement sensor. The ShockPulse Measurement sensor is designed and adapted to provide apre-determined mechanical resonance frequency, as described in furtherdetail below.

This feature of the Shock Pulse Measurement sensor advantageouslyrenders repeatable measurement results in that the output signal from aShock Pulse Measurement sensor has a stable resonance frequencysubstantially independent of the physical path between the shock pulsesignal source and the shock pulse sensor. Moreover, mutually differentindividual shock pulse sensors provide a very small, if any, deviationin resonance frequency.

An advantageous effect of this is that signal processing is simplified,in that filters need not be individually adjusted, in contrast to thecase described above when vibration sensors are used. Moreover, theamplitude response from shock pulse sensors is well defined such that anindividual measurement provides reliable information when measurement isperformed in accordance with appropriate measurement methods defined byS.P.M. Instrument AB.

FIG. 2D illustrates a measuring signal amplitude generated by a shockpulse sensor 10, and FIG. 2E illustrates a measuring signal amplitudegenerated by a vibration sensor 10. Both sensors have been exerted tothe same series of mechanical shocks without the typical low frequencysignal content. In FIGS. 2D and 2E, the vertical axes representamplitude of an analogue electrical signal generated by the respectivesensor, and the horizontal axes represent time. In both of FIGS. 2D and2E, the respective analogue measurement signals S_(EA) include avibration signal signature S_(D) having

-   -   a vibration frequency f_(SEA),    -   at least one vibration signal repetition frequency f_(D), being        the inverse of the time period T_(D) between two temporally        adjacent vibration signal signatures S_(D), and    -   a vibration signal amplitude.

According to an embodiment of the invention the sensor is a Shock PulseMeasurement sensor. FIG. 3 is a simplified illustration of a Shock PulseMeasurement sensor 10 according to an embodiment of the invention.According to this embodiment the sensor comprises a part 110 having acertain mass or weight and a piezo-electrical element 120. Thepiezo-electrical element 120 is somewhat flexible so that it cancontract and expand when exerted to external force. The piezo-electricalelement 120 is provided with electrically conducting layers 130 and 140,respectively, on opposing surfaces. As the piezo-electrical element 120contracts and expands it generates an electric signal which is picked upby the conducting layers 130 and 140. Accordingly, a mechanicalvibration is transformed into an analogue electrical measurement signalS_(EA), which is delivered on output terminals 145, 150.

The piezo-electrical element 120 may be positioned between the weight110 and a surface 160 which, during operation, is physically attached tothe measuring point 12, as illustrated in FIG. 3.

The Shock Pulse Measurement sensor 10 has a resonance frequency thatdepends on the mechanical characteristics for the sensor, such as themass m of weight part 110 and the resilience of piezo-electrical element120. Hence, the piezo-electrical element has an elasticity and a springconstant k. The mechanical resonance frequency f_(RM) for the sensor istherefore also dependent on the mass m and the spring constant k.

According to an embodiment of the invention the mechanical resonancefrequency f_(RM) for the sensor can be determined by the equationfollowing equation:

f _(RM)=1/(2π)√(k/m)   (eq1)

According to another embodiment the actual mechanical resonancefrequency for a Shock Pulse Measurement sensor 10 may also depend onother factors, such as the nature of the attachment of the sensor 10 tothe body of the machine 6.

The resonant Shock Pulse Measurement sensor 10 is thereby particularlysensitive to vibrations having a frequency on or near the mechanicalresonance frequency f_(RM). The Shock Pulse Measurement sensor 10 may bedesigned so that the mechanical resonance frequency f_(RM) is somewherein the range from 28 kHz to 37 kHz. According to another embodiment themechanical resonance frequency f_(RM) is somewhere in the range from 30kHz to 35 kHz.

Accordingly the analogue electrical measurement signal has an electricalamplitude which may vary over the frequency spectrum. For the purpose ofdescribing the theoretical background, it may be assumed that if theShock Pulse Measurement sensor 10 were exerted to mechanical vibrationswith identical amplitude in all frequencies from e.g. 1 Hz to e.g. 200000 kHz, then the amplitude of the analogue signal S_(EA) from the ShockPulse Measurement Sensor will have a maximum at the mechanical resonancefrequency f_(RM), since the sensor will resonate when being “pushed”with that frequency.

With reference to FIG. 2B, the conditioning circuit 43 receives theanalogue signal S_(EA). The conditioning circuit 43 may be designed tobe an impedance adaption circuit designed to adapt the input impedanceof the A/D-converter as seen from the sensor terminals 145,150 so thatan optimum signal transfer will occur. Hence, the conditioning circuit43 may operate to adapt the input impedance Z_(in) as seen from thesensor terminals 145,150 so that a maximum electric power is deliveredto the A/D-converter 44. According to an embodiment of the conditioningcircuit 43 the analogue signal S_(EA) is fed to the primary winding of atransformer, and a conditioned analogue signal is delivered by asecondary winding of the transformer. The primary winding has n1 turnsand the secondary winding has n2 turns, the ratio n1/n2=n₁₂. Hence, theA/D converter 44 is coupled to receive the conditioned analogue signalfrom the conditioning circuit 43. The A/D converter 44 has an inputimpedance Z₄₄, and the input impedance of the A/D-converter as seen fromthe sensor terminals 145,150 will be (n1/n2)²*Z₄₄, when the conditioningcircuit 43 is coupled in between the sensor terminals 145,150 and theinput terminals of the A/D converter 44.

The A/D converter 44 samples the received conditioned analogue signalwith a certain sampling frequency f_(s) so as to deliver a digitalmeasurement data signal S_(MD) having said certain sampling frequencyf_(s) and wherein the amplitude of each sample depends on the amplitudeof the received analogue signal at the moment of sampling.

According to embodiments of the invention the digital measurement datasignal S_(MD) is delivered to a means 180 for digital signal processing(See FIG. 5).

According to an embodiment of the invention the means 180 for digitalsignal processing comprises the data processor 50 and program code forcausing the data processor 50 to perform digital signal processing.According to an embodiment of the invention the processor 50 is embodiedby a Digital Signal Processor. The Digital Signal Processor may also bereferred to as a DSP.

With reference to FIG. 2A, the data processing means 50 is coupled to amemory 60 for storing said program code. The program memory 60 ispreferably a non-volatile memory. The memory 60 may be a read/writememory, i.e. enabling both reading data from the memory and writing newdata onto the memory 60. According to an embodiment the program memory60 is embodied by a FLASH memory. The program memory 60 may comprise afirst memory segment 70 for storing a first set of program code 80 whichis executable so as to control the analysis apparatus 14 to performbasic operations (FIG. 2A and FIG. 4). The program memory may alsocomprise a second memory segment 90 for storing a second set of programcode 94. The second set of program code 94 in the second memory segment90 may include program code for causing the analysis apparatus toprocess the detected signal, or signals, so as to generate apre-processed signal or a set of pre-processed signals. The memory 60may also include a third memory segment 100 for storing a third set ofprogram code 104. The set of program code 104 in the third memorysegment 100 may include program code for causing the analysis apparatusto perform a selected analysis function 105. When an analysis functionis executed it may cause the analysis apparatus to present acorresponding analysis result on user interface 106 or to deliver theanalysis result on port 16 (See FIG. 1 and FIG. 2A and FIG. 7).

The data processing means 50 is also coupled to a read/write memory 52for data storage. Moreover, the data processing means 50 may be coupledto an analysis apparatus communications interface 54. The analysisapparatus communications interface 54 provides for bi-directionalcommunication with a measuring point communication interface 56 which isattachable on, at or in the vicinity of the measuring point on themachine.

The measuring point 12 may comprise a connection coupling 32, a readableand writeable information carrier 58, and a measuring pointcommunication interface 56.

The writeable information carrier 58, and the measuring pointcommunication interface 56 may be provided in a separate device 59placed in the vicinity of the stud 30, as illustrated in FIG. 2.Alternatively the writeable information carrier 58, and the measuringpoint communication interface 56 may be provided within the stud 30.This is described in more detail in WO 98/01831, the content of which ishereby incorporated by reference.

The system 2 is arranged to allow bidirectional communication betweenthe measuring point communication interface 56 and the analysisapparatus communication interface 54. The measuring point communicationinterface 56 and the analysis apparatus communication interface 54 arepreferably constructed to allow wireless communication. According to anembodiment the measuring point communication interface and the analysisapparatus communication interface are constructed to communicate withone another by radio frequency (RF) signals. This embodiment includes anantenna in the measuring point communication interface 56 and anotherantenna the analysis apparatus communication interface 54.

FIG. 4 is a simplified illustration of an embodiment of the memory 60and its contents. The simplified illustration is intended to conveyunderstanding of the general idea of storing different program functionsin memory 60, and it is not necessarily a correct technical teaching ofthe way in which a program would be stored in a real memory circuit. Thefirst memory segment 70 stores program code for controlling the analysisapparatus 14 to perform basic operations. Although the simplifiedillustration of FIG. 4 shows pseudo code, it is to be understood thatthe program code 80 may be constituted by machine code, or any levelprogram code that can be executed or interpreted by the data processingmeans 50 (FIG. 2A).

The second memory segment 90, illustrated in FIG. 4, stores a second setof program code 94. The program code 94 in segment 90, when run on thedata processing means 50, will cause the analysis apparatus 14 toperform a function, such as a digital signal processing function. Thefunction may comprise an advanced mathematical processing of the digitalmeasurement data signal S_(MD). According to embodiments of theinvention the program code 94 is adapted to cause the processor means 50to perform signal processing functions described in connection withFIGS. 5, 6, 9, 10, 11A, 11B, 12A, 12B, 13A-C, 14A, 14B, 15A and/or FIG.16 in this document.

As mentioned above in connection with FIG. 1, a computer program forcontrolling the function of the analysis apparatus may be downloadedfrom the server computer 20. This means that theprogram-to-be-downloaded is transmitted to over the communicationsnetwork 18. This can be done by modulating a carrier wave to carry theprogram over the communications network 18. Accordingly the downloadedprogram may be loaded into a digital memory, such as memory 60 (SeeFIGS. 2A and 4). Hence, a signal processing program 94 and or ananalysis function program 104, 105 may be received via a communicationsport, such as port 16 (FIGS. 1 & 2A), so as to load it into memory 60.Similarly, a signal processing program 94 and or an analysis functionprogram 104, 105 may be received via communications port 29B (FIG. 1),so as to load it into a program memory location in computer 26B or indatabase 22B.

An aspect of the invention relates to a computer program product, suchas a program code means 94 and/or program code means 104, 105 loadableinto a digital memory of an apparatus. The computer program productcomprising software code portions for performing signal processingmethods and/or analysis functions when said product is run on a dataprocessing unit 50 of an apparatus for analysing the condition of amachine. The term “run on a data processing unit” means that thecomputer program plus the data processing unit carries out a method ofthe kind described in this document.

The wording “a computer program product, loadable into a digital memoryof a condition analysing apparatus” means that a computer program can beintroduced into a digital memory of a condition analysing apparatus soas achieve a condition analysing apparatus programmed to be capable of,or adapted to, carrying out a method of the kind described above. Theterm “loaded into a digital memory of a condition analysing apparatus”means that the condition analysing apparatus programmed in this way iscapable of, or adapted to, carrying out a method of the kind describedabove.

The above mentioned computer program product may also be loadable onto acomputer readable medium, such as a compact disc or DVD. Such a computerreadable medium may be used for delivery of the program to a client.

According to an embodiment of the analysis apparatus 14 (FIG. 2A), itcomprises a user input interface 102, whereby an operator may interactwith the analysis apparatus 14. According to an embodiment the userinput interface 102 comprises a set of buttons 104. An embodiment of theanalysis apparatus 14 comprises a user output interface 106. The useroutput interface may comprise a display unit 106. The data processingmeans 50, when it runs a basic program function provided in the basicprogram code 80, provides for user interaction by means of the userinput interface 102 and the display unit 106. The set of buttons 104 maybe limited to a few buttons, such as for example five buttons, asillustrated in FIG. 2A. A central button 107 may be used for an ENTER orSELECT function, whereas other, more peripheral buttons may be used formoving a cursor on the display 106. In this manner it is to beunderstood that symbols and text may be entered into the apparatus 14via the user interface. The display unit 106 may, for example, display anumber of symbols, such as the letters of alphabet, while the cursor ismovable on the display in response to user input so as to allow the userto input information.

FIG. 5 is a schematic block diagram of an embodiment of the analysisapparatus 14 at a client location 4 with a machine 6 having a movableshaft 8. The sensor 10, which may be a Shock Pulse Measurement Sensor,is shown attached to the body of the machine 6 so as to pick upmechanical vibrations and so as to deliver an analogue measurementsignal S_(EA) indicative of the detected mechanical vibrations to thesensor interface 40. The sensor interface 40 may be designed asdescribed in connection with FIG. 2A or 2B. The sensor interface 40delivers a digital measurement data signal S_(MD) to a means 180 fordigital signal processing.

The digital measurement data signal S_(MD) has a sampling frequencyf_(s), and the amplitude value of each sample depends on the amplitudeof the received analogue measurement signal S_(EA) at the moment ofsampling. According to an embodiment the sampling frequency f_(s) of thedigital measurement data signal S_(MD) may be fixed to a certain valuef_(s), such as e.g. f_(s)=102 400 Hz. The sampling frequency f_(s) maybe controlled by a clock signal delivered by a clock 190, as illustratedin FIG. 5. The clock signal may also be delivered to the means 180 fordigital signal processing. The means 180 for digital signal processingcan produce information about the temporal duration of the receiveddigital measurement data signal S_(MD) in response to the receiveddigital measurement data signal S_(MD), the clock signal and therelation between the sampling frequency f_(s) and the clock signal,since the duration between two consecutive sample values equalsT_(s)=1/f_(s).

According to embodiments of the invention the means 180 for digitalsignal processing includes a pre-processor 200 for performing apre-processing of the digital measurement data signal S_(MD) so as todeliver a pre-processed digital signal S_(MDP) on an output 210. Theoutput 210 is coupled to an input 220 of an evaluator 230. The evaluator230 is adapted to evaluate the pre-processed digital signal S_(MDP) soas to deliver a result of the evaluation to a user interface 106.Alternatively the result of the evaluation may be delivered to acommunication port 16 so as to enable the transmission of the resulte.g. to a control computer 33 at a control site 31 (See FIG. 1).

According to an embodiment of the invention, the functions described inconnection with the functional blocks in means 180 for digital signalprocessing, pre-processor 200 and evaluator 230 may be embodied bycomputer program code 94 and/or 104 as described in connection withmemory blocks 90 and 100 in connection with FIG. 4 above.

A user may require only a few basic monitoring functions for detectionof whether the condition of a machine is normal or abnormal. Ondetecting an abnormal condition, the user may call for specializedprofessional maintenance personnel to establish the exact nature of theproblem, and for performing the necessary maintenance work. Theprofessional maintenance personnel frequently needs and uses a broadrange of evaluation functions making it possible to establish the natureof, and/or cause for, an abnormal machine condition. Hence, differentusers of an analysis apparatus 14 may pose very different demands on thefunction of the apparatus. The term Condition Monitoring function isused in this document for a function for detection of whether thecondition of a machine is normal or somewhat deteriorated or abnormal.The term Condition Monitoring function also comprises an evaluationfunction making it possible to establish the nature of, and/or causefor, an abnormal machine condition.

Examples of Machine Condition Monitoring functions

The condition monitoring functions F1, F2 . . . Fn includes functionssuch as: vibration analysis, shock pulse measuring, Peak level analysis,spectrum analysis of shock pulse measurement data, Fast FourierTransformation of vibration measurement data, graphical presentation ofcondition data on a user interface, storage of condition data in awriteable information carrier on said machine, storage of condition datain a writeable information carrier in said apparatus, tachometering,imbalance detection, and misalignment detection.

According to an embodiment the apparatus 14 includes the followingfunctions:

F1=vibration analysis;

F2=shock pulse measuring,

F3=Peak level analysis

F4=spectrum analysis of shock pulse measurement data,

F5=Fast Fourier Transformation of vibration measurement data,

F6=graphical presentation of condition data on a user interface,

F7=storage of condition data in a writeable information carrier on saidmachine,

F8=storage of condition data in a writeable information carrier 52 insaid apparatus,

F9=tachometering,

F10=imbalance detection, and

F11=misalignment detection.

F12=Retrieval of condition data from a writeable information carrier 58on said machine.

F13=Performing Peak level analysis F3 and performing function F12“Retrieval of condition data from a writeable information carrier 58 onsaid machine” so as to enable a comparison or trending based on currentPeak level data and historical Peak level data.

F14=Retrieval of identification data from a writeable informationcarrier 58 on said machine.

Embodiments of the function F7 “storage of condition data in a writeableinformation carrier on said machine”, and F13 vibration analysis andretrieval of condition data is described in more detail in WO 98/01831,the content of which is hereby incorporated by reference.

The peak level analysis F3 may be performed on the basis of theenveloped time domain signal S_(ENV) delivered by an enveloper 250. Thesignal S_(ENV) is also referred to as S_(MDP)

The peak level analysis F3 is adapted to monitor the signal for theduration of a peak monitoring period T_(PM) for the purpose ofestablishing the maximum amplitude level.

The peak amplitude may be indicative of Oil film thickness in amonitored bearing. Hence, the detected peak amplitude may be indicativeof separation between the metal surfaces in the rolling interface. Theoil film thickness may depend on lubricant supply and/or on alignment ofthe shaft. Moreover, the oil film thickness may depend on the load onthe shaft, i.e. on the force with which metal surfaces are pressedtogether, the metal surfaces being e.g. that of a bearing and that of ashaft.

The actual detected value of the maximum amplitude level may also dependon the mechanical state of the bearing surfaces, .i.e the condition ofthe bearing assembly. Accordingly, the detected value of the maximumamplitude level may depend on roughness of the metal surfaces in therolling interface, and/or damage to a metal surface in the rollinginterface. The detected value of the maximum amplitude level may alsodepend on the occurrence of a loose particle in the bearing assembly.

FIG. 6A illustrates a schematic block diagram of an embodiment of thepre-processor 200 according to an embodiment of the present invention.In this embodiment the digital measurement data signal S_(MD) is coupledto a digital band pass filter 240 having a lower cutoff frequencyf_(LC), an upper cutoff frequency f_(UC) and passband bandwidth betweenthe upper and lower cutoff frequencies.

The output from the digital band pass filter 240 is connected to adigital enveloper 250. According to an embodiment of the invention thesignal output from the enveloper 250 is delivered to an output 260. Theoutput 260 of the pre-processor 200 is coupled to output 210 of digitalsignal processing means 180 for delivery to the input 220 of evaluator230.

The upper and lower cutoff frequencies of the digital band pass filter240 may selected so that the frequency components of the signal S_(MD)at the resonance frequency f_(RM) for the sensor are in the passbandbandwidth. As mentioned above, an amplification of the mechanicalvibration is achieved by the sensor being mechanically resonant at theresonance frequency f_(RM). Accordingly the analogue measurement signalS_(EA) reflects an amplified value of the vibrations at and around theresonance frequency f_(RM). Hence, the band pass filter according to theFIG. 6 embodiment advantageously suppresses the signal at frequenciesbelow and above resonance frequency f_(RM), so as to further enhance thecomponents of the measurement signal at the resonance frequency f_(RM).Moreover, the digital band pass filter 240 advantageously furtherreduces noise inherently included in the measurement signal, since anynoise components below the lower cutoff frequency f_(LC), and aboveupper cutoff frequency f_(UC) are also eliminated or reduced. Hence,when using a resonant Shock Pulse Measurement sensor 10 having amechanical resonance frequency f_(RM) in a range from a lowest resonancefrequency value f_(RML) to a highest resonance frequency value f_(RMU)the digital band pass filter 240 may be designed to having a lowercutoff frequency f_(LC)=f_(RML), and an upper cutoff frequencyf_(UC)=f_(RMU). According to an embodiment the lower cutoff frequencyf_(LC)=f_(RML)=28 kHz, and the upper cutoff frequency f_(UC)=f_(RMU)=37kHz.

According to another embodiment the mechanical resonance frequencyf_(RM) is somewhere in the range from 30 kHz to 35 kHz, and the digitalband pass filter 240 may then be designed to having a lower cutofffrequency f_(LC)=30 kHz and an upper cutoff frequency f_(UC)=35 kHz.

According to another embodiment the digital band pass filter 240 may bedesigned to have a lower cutoff frequency f_(LC) being lower than thelowest resonance frequency value f_(RM), and an upper cutoff frequencyf_(UC) being higher than the highest resonance frequency value f_(RMU).For example the mechanical resonance frequency f_(RM) may be a frequencyin the range from 30 kHz to 35 kHz, and the digital band pass filter 240may then be designed to having a lower cutoff frequency f_(LC)=17 kHz,and an upper cutoff frequency f_(UC)=36 kHz.

Accordingly, the digital band pass filter 240 may deliver a passbanddigital measurement data signal S_(F) having an advantageously lowout-of-band noise content and reflecting mechanical vibrations in thepassband. The passband digital measurement data signal S_(F) may bedelivered to an enveloper 250.

The digital enveloper 250 accordingly receives the passband digitalmeasurement data signal S_(F) which may reflect a signal having positiveas well as negative amplitudes. With reference to FIG. 6A, the receivedsignal is rectified by a digital rectifier 270, and the rectified signalmay be filtered by an optional low pass filter 280 so as to produce adigital envelop signal S_(ENV).

Accordingly, the signal S_(ENV) is a digital representation of anenvelope signal being produced in response to the filtered measurementdata signal S_(F). According to some embodiments of the invention theoptional low pass filter 280 may be eliminated.

According to the FIG. 6A embodiment of the invention the signal S_(ENV)is delivered to the output 260 of pre-processor 200. Hence, according toan embodiment of the invention the pre-processed digital signal S_(MDP)delivered on the output 210 (FIG. 5) is the digital envelop signalS_(ENV).

Whereas prior art analogue devices for generating an envelop signal inresponse to a measurement signal employs an analogue rectifier whichinherently leads to a biasing error being introduced in the resultingsignal, the digital enveloper 250 will advantageously produce a truerectification without any biasing errors. Accordingly, the digitalenvelop signal S_(ENV) will have a good Signal-to-Noise Ratio, since thesensor being mechanically resonant at the resonance frequency in thepassband of the digital band pass filter 240 leads to a high signalamplitude and the signal processing being performed in the digitaldomain eliminates addition of noise and eliminates addition of biasingerrors.

With reference to FIG. 5 the pre-processed digital signal S_(MDP) isdelivered to input 220 of the evaluator 230.

According to another embodiment, the filter 240 is a high pass filterhaving a cut-off frequency f_(LC). This embodiment simplifies the designby replacing the band-pass filter with a high-pass filter 240, therebyleaving the low pass filtering to another low pass filter downstream,such as the low pass filter 280. The cut-off frequency f_(LC) of thehigh pass filter 240 is selected to approximately the value of thelowest expected mechanical resonance frequency value f_(RMU) of theresonant Shock Pulse Measurement sensor 10. When the mechanicalresonance frequency f_(RM) is somewhere in the range from 30 kHz to 35kHz, the high pass filter 240 may be designed to having a lower cutofffrequency f_(LC)=30 kHz. The high-pass filtered signal is then passed tothe rectifier 270 and on to the low pass filter 280. According to anembodiment it should be possible to use sensors 10 having a resonancefrequency somewhere in the range from 20 kHz to 35 kHz. In order toachieve this, the high pass filter 240 may be designed to having a lowercutoff frequency f_(LC)=20 kHz.

FIG. 6B illustrates an embodiment according to which the digital bandpass filter 240 delivers the filtered signal S_(F) to the digitalrectifier 270, and the rectifier 270 delivers the rectified signal S_(R)directly to a condition analyzer 290 (See FIG. 7 in conjunction withFIG. 6B).

FIG. 7 illustrates an embodiment of the evaluator 230 (See also FIG. 5).The FIG. 7 embodiment of the evaluator 230 includes the conditionanalyser 290 adapted to receive a pre-processed digital signal S_(MDP)indicative of the condition of the machine 6. The condition analyser 290can be controlled to perform a selected condition analysis function 105by means of a selection signal delivered on a control input 300.Examples of condition analysis functions 105 are schematicallyillustrated as boxes in FIG. 7. The selection signal delivered oncontrol input 300 may be generated by means of user interaction with theuser interface 102 (See FIG. 2A).

As mentioned above, the analysis apparatus 14 may include a Peak levelanalysis function F3, 105 (See FIG. 4 & FIG. 7).

According to an embodiment of the invention the Peak level analysisfunction may be performed by the condition analyser 290 in response toactivation via control input 300. In response to the peak level analysisactivation signal, the analyzer 290 will activate a peak level analyzerF3, 105 (See FIG. 7), and the digital measurement signal SMDP will bepassed to an input of the peak level analyzer F3, 105.

The peak level analyzer F3, 105 is adapted to monitor the signal for avariably settable duration (TMeas) of a measuring session for thepurpose of collecting a number of peak amplitude values.

As mentioned above, the peak amplitude detected in the measurementsignal may, when the peak amplitude value originates from a mechanicalvibration in the monitored machine, be indicative of the condition ofthe machine. When a bearing assembly is monitored, the peak amplitudevalue may be indicative of the condition of the bearing assembly. Infact, the peak amplitude value may be indicative of Oil film thicknessin a monitored bearing. Hence, the detected peak amplitude may beindicative of separation between the metal surfaces in the rollinginterface. The oil film thickness may depend on lubricant supply and/oron alignment of the shaft. Moreover, the oil film thickness may dependon the load on the shaft, i.e. on the force with which metal surfacesare pressed together, the metal surfaces being e.g. that of a bearingand that of a shaft. The actual detected value of the peak amplitudelevels may also depend on the mechanical state of the bearing surfaces.The rotation of the rotatable machine part may cause a mechanicalvibration V_(MD) indicative of a deteriorated condition in thatrotatable machine part.

Tests have indicated that the detected peak amplitude levels for arotational part often varies, i.e. each revolution of a rotational shaftdoes not produce identical peak levels. After careful study of suchamplitude levels the inventor concluded that

-   -   the amplitude levels emanating from rotation of a monitored        rotational part closely follow the normal distribution, also        referred to as the Gaussian distribution; and that    -   it is advantageous to record the amplitude levels during an        uninterrupted variably settable duration T_(Meas), preferably        longer than one second, in order to collect a number of peak        amplitude values which may be used for a reliable determination        of the condition of the monitored rotational part. According to        a preferred embodiment the variably settable duration T_(Meas)        is longer than 1.3 seconds. According to an embodiment, the        variably settable duration T_(Meas) is longer than three seconds        when switch 909B is also operated so as to concurrently produce        a transformed signal.

In this context, it should be noted that the normal distribution is aprobability distribution that describes data that cluster around themean. The graph of the associated probability density function isbell-shaped, with a peak at the mean, and is known as the Gaussianfunction or bell curve.

FIG. 8 is a schematic block diagram illustrating an improved apparatus14. The illustrated apparatus 14 includes a transducer 10 for convertingmechanical vibrations in a bearing to analogue electrical oscillationsS_(EA). The presently preferred transducer may comprise a resonantpiezoelectric accelerometer, as described above in this document. Theanalogue signal S_(EA) from the transducer 10 may be delivered to aconditioning circuit 43 which may be coupled to receive the analoguesignal S_(EA), and an A/D converter 44 may be coupled to receive theconditioned analogue signal from the conditioning circuit 43. The A/Dconverter 44 samples the received conditioned analogue signal with acertain sampling frequency f_(s) so as to deliver a digital measurementdata signal S_(MD) having said certain sampling frequency f_(s) andwherein the amplitude of each sample depends on the amplitude of thereceived analogue signal at the moment of sampling.

The digital measurement data signal S_(MD) may be filtered, e.g. by adigital filter 240, so that the resulting signal has an upper frequencylimit value f_(SEAmax) corresponding to an upper cutoff filter frequencyf_(UC). The digital filter 240 may be a digital band pass filter 240 asdescribed in connection with FIG. 6A and/or FIG. 6B.

A digital rectifier 270 may be provided to perform a rectification ofthe digital signal so as to generate a rectified digital signal S_(R)dependent on said digital measurement signal S_(MD). According to apreferred embodiment the digital rectifier 270 is adapted to perform afull-wave rectification so as to generate a rectified digital signalS_(R) dependent on said digital measurement signal S_(MD) includingabsolute values of the resulting sequence of sample values.

A digital peak value detector 310 may be adapted to generate output peakvalues A_(PO) on an output 315 dependent on said sequence of samplevalues S_(MD), S_(R).

The detected signal peaks or detected signal peak values A_(PO) may bedelivered from the peak detector output 315 to an input 840 of a loggenerator 850. The log generator 850 is adapted to generate thelogarithmic amplitude values corresponding to the amplitude of thereceived detected signal peaks or detected signal peak values A_(PO).Hence, an output 860 of log generator 850 is adapted to deliverlogarithmic amplitude values.

A value sorter 870, also referred to as peak value discriminator 870, isadapted to receive the logarithmic amplitude values and to sort thereceived the logarithmic amplitude values into amplitude binscorresponding to the received logarithmic amplitude values during ameasuring session. Hence, the value sorter 870 may be adapted to deliversorted amplitude values A_(PO), e.g. in the form of a table 470 at theend of a measuring session. The table 470 may be a table histogram 470and/or cumulative histogram table 530, as discussed and illustrated inconnection with FIGS. 9 and/or 11 below.

A measuring session controller 904 may be provided to control a variablysettable duration T_(Meas) of the measuring session. The measuringsession controller 904 may provide a control signal T_(control) so as toturn on switches 909A and 909B simultaneously, or substantiallysimultaneously, and so as to turn off the switches 909A and 909Bsimultaneously, or substantially simultaneously. In such a manner theswitches 909A and 909B may be switched on at the start of the measuringsession duration T_(Meas), and the switches 909A and 909B may beswitched off at the end of the measuring session duration T_(Meas). Inthis manner the peak value discriminator 870 will operate for theduration of the measuring session duration T_(Meas), and at the end ofthe measuring session duration T_(Meas) the relevant time valueT_(MeasV), counted e.g as an amount of seconds, is stored in associationwith the table 470.

The measuring session duration T_(Meas) may be settable by a user viathe user interface. Alternatively, the measuring session durationT_(Meas) may be settable in dependence on the duration necessary forobtaining a desired frequency resolution by the Fast Fourier Transformer1020.

FIG. 9 is a schematic illustration of plural memory positions arrangedas a table 470, and suitable for storage of data to be collected. Thetable 470 may be stored in the memory 52 (FIG. 2A) or in a memoryinternal to the processor 50.

FIG. 10 illustrates a histogram having plural amplitude bins 500, eachamplitude bin representing an amplitude level A_(r). The number ofamplitude bins may be set to a suitable number by the user, via userinterface 102 (FIG. 2A). FIG. 10 illustrates a number of amplitude binsalong one axis 480, and occurrence of detected peak amplitude valuesalong another axis 490. However, in the illustration of FIG. 10 novalues have been plotted in the histogram. The amplitude axis 480 mayhave a certain resolution, which may also be settable by the user, viathe user interface 102. Alternatively the resolution of the amplitudeaxis 480 may be preset. According to an embodiment the resolution of theamplitude axis 480 may be set to 0.2 dB, and the amplitudes to berecorded may span from a lowest amplitude of A_(r1)=−50 dB to a highestamplitude value A_(r750)=+100 dB.

With reference to FIG. 9, the illustrated table 470 is a representationof the histogram shown in FIG. 10, having amplitude bins 500,individually referred to by references r1 to r750, each amplitude bin r1. . . r750 representing an amplitude level A_(r). The table 470 alsoincludes memory positions 510 for amplitude values A, and memorypositions 520 for variables N_(r) reflecting the occurrence.

Bin r1 is associated with an amplitude value A_(r1) and with a memoryposition for a variable N_(r1) for storing a value indicating how manytimes the amplitude Ar1 has been detected. Before the start of ameasuring session, all the occurrence variables N_(r1) to N_(r750) maybe set to zero (0). Thereafter the measuring session may begin.

During the measuring session said detected peak amplitude values aresorted into corresponding amplitude ranges 500 so as to reflectoccurrence N of detected peak amplitude values Ap within said pluralityof amplitude ranges 500 (See FIG. 9).

The duration of the measurement session is controlled by measuringsession controller 904, in dependence of time information provided by aclock 190 (FIG. 5).

At the end of the session, the switch 909A turns off, so that no morepeak amplitude values can be added in the table. The occurrence valuesN_(r) in the respective bins are divided by the relevant time valueT_(MeasV), counted e.g as an amount of seconds, so as to obtain anaverage occurrence frequency value f_(C), expressed e.g. as pulses persecond for each of the amplitude bins. Since these average values arecounted as an average for the complete duration of the measuringsession, the resulting value has been found to be advantageouslyreliable.

According to an embodiment, two occurrence frequency values f_(C1) andf_(C2) are to be identified. According to a preferred embodiment, thefirst occurrence frequency value f_(C1) corresponds to a mean value ofabout 40 peak values per second, and the second occurrence frequencyvalue f_(C2) corresponds to a mean value of about 1000 peak values persecond.

With reference to FIG. 8, the apparatus 14 further comprises

-   -   a decimator 1010 adapted to generate a decimated digital signal        S_(RED) in dependence of said digital measurement signal S_(MD),        S_(R) so that the decimated digital signal S_(RED) has a reduced        sampling frequency f_(SR); f_(SR1); and    -   a Fourier Transformer 1020 adapted to generate a transformed        signal S_(FT) in dependence of a selected second temporal        portion of said decimated digital signal S_(RED); so that said        transformed signal S_(FT) is indicative of said vibration signal        repetition frequency f_(D). The apparatus may be arranged to        coordinate the generation of said transformed signal S_(FT) with        the generation of the first condition value LR_(D) so that the        selected second temporal portion of said decimated digital        signal S_(RED) is based substantially on said selected first        temporal portion of the digital measurement signal S_(MD), and        so that said selected first temporal portion of the digital        measurement signal S_(MD) is generated during the variably        settable duration T_(Meas) of said measuring session.

FIG. 11 is an illustration of a cumulative histogram table 530corresponding to the histogram table of FIG. 9. The cumulative histogramtable of FIG. 11 includes the same number of amplitude range bins as theFIG. 9 table. In the cumulative histogram the occurrence N′ is reflectedas the number of occurrences of detected peaks having an amplitudehigher than the amplitude A_(r)′ of associated amplitude bin r. Thisadvantageously provides for a smoother curve when the cumulativehistogram is plotted. Whereas the ‘ordinary’ histogram reflecting alimited number of observations will reflect a lack of observations N atan amplitude bin as a notch or dent at that bin, the cumulativehistogram will provide a smoother curve, which makes is more suitablefor use in estimating occurrence at one amplitude level based on theobservation of occurrences at other amplitude levels.

According to an embodiment of the invention, the data of the table ofFIG. 9 may advantageously be arranged as a cumulative histogram 530, andthe two occurrence frequency values f_(C1) and f_(C2) may be identifiedfrom the cumulative histogram 530. According to an embodiment, the firstoccurrence frequency value f_(C1) may correspond to a mean value ofabout 40 peak values per second, and the second occurrence frequencyvalue f_(C2) may correspond to a mean value of about 1000 peak valuesper second.

FIG. 12 is a schematic block diagram of another embodiment of theanalysis apparatus 14. The illustrated apparatus 14 includes atransducer 10 for converting mechanical vibrations in a bearing toanalogue electrical oscillations S_(EA). The presently preferredtransducer may comprise a resonant piezoelectric accelerometer, asdescribed above in this document. The analogue signal S_(EA) from thetransducer 10 may be delivered to a conditioning circuit 43 which may becoupled to receive the analogue signal S_(EA), and an A/D converter 44may be coupled to receive the conditioned analogue signal from theconditioning circuit 43. The A/D converter 44 samples the receivedconditioned analogue signal with a certain sampling frequency f_(s) soas to deliver a digital measurement data signal S_(MD) having saidcertain sampling frequency f_(s) and wherein the amplitude of eachsample depends on the amplitude of the received analogue signal at themoment of sampling.

The digital measurement data signal S_(MD) may be filtered, e.g. by adigital filter 240, so that the resulting digitally filtered signalS_(F) has an upper frequency limit value f_(SEAmax) corresponding to anupper cutoff filter frequency f_(UC). The digital filter 240 may be adigital band pass filter 240 as described in connection with FIG. 6Aand/or FIG. 6B.

A digital rectifier 270 may be provided to perform a rectification ofthe digital signal so as to generate a rectified digital signal S_(R).According to a preferred embodiment the digital rectifier 270 is adaptedto perform a full-wave rectification so as to generate a rectifieddigital signal S_(R). According to a most preferred embodiment, asillustrated in FIG. 12, the digital rectifier 270 is adapted to performa full-wave rectification of the digitally filtered signal so as togenerate the rectified digital signal S_(R). The rectified signal S_(R)may be delivered to a digital peak value detector 310 as well as to anenveloper 250.

The digital peak value detector 310 may be adapted to generate outputpeak values A_(PO) on a peak detector output 315 dependent on saidsequence of sample values S_(MD), S_(R), S_(F).

The detected signal peaks or detected signal peak values A_(PO) may bedelivered from the peak detector output 315 to an input 840 of a loggenerator 850. The log generator 850 is adapted to generate thelogarithmic amplitude values corresponding to the amplitude of thereceived detected signal peaks or detected signal peak values A_(PO).Hence, an output 860 of log generator 850 is adapted to deliverlogarithmic amplitude values.

A value sorter 870, also referred to as peak value discriminator 870, isadapted to receive the logarithmic amplitude values and to sort thereceived the logarithmic amplitude values into amplitude binscorresponding to the received logarithmic amplitude values during ameasuring session. Hence, the value sorter 870 may be adapted to deliversorted amplitude values A_(PO), e.g. in the form of a table 470 at theend of a measuring session. The table 470 may be a table histogram 470and/or a cumulative histogram table 530, as discussed and illustrated inconnection with FIGS. 9 and/or 11 below.

A measuring session controller 904 may be provided to control a variablysettable duration T_(Meas) of the measuring session. The measuringsession controller 904 may provide a control signal T_(control) so as toturn on switches 909A and 909B simultaneously, or substantiallysimultaneously, and so as to turn off the switches 909A and 909Bsimultaneously, or substantially simultaneously. In such a manner theswitches 909A and 909B may be switched on at the start of the measuringsession duration T_(Meas), and the switches 909A and 909B may beswitched off at the end of the measuring session duration T_(Meas). Inthis manner the peak value discriminator 870 will operate for theduration of the measuring session duration T_(Meas), and at the end ofthe measuring session duration T_(Meas) the relevant time valueT_(MeasV), counted e.g as an amount of seconds, may be stored inassociation with the table 470, 530. The relevant time value T_(MeasV)may be stored in a memory 910, as illustrated in FIG. 12. The memory 910may also store the histogram table 470 and/or cumulative histogram table530 delivered from the value sorter 870. The memory 910 may be embodiedby the memory 52 (FIG. 2A) or it may be embodied by a memory internal tothe processor 50.

The measuring session duration T_(Meas) may be settable by a user viathe user interface 102 (see FIG. 2A). Alternatively, the measuringsession duration T_(Meas) may be settable in dependence on the durationnecessary for obtaining a desired frequency resolution by the FastFourier Transformer 1020.

At the end of the measuring session, the switch 909A turns off, so thatno more peak amplitude values can be added in the histogram table 470and/or cumulative histogram table 530. A condition value generator 1030is adapted to receive the relevant time value T_(MeasV) and thehistogram table 470 and/or cumulative histogram table 530 from the valuesorter 870. The condition value generator 1030 operates to divide theoccurrence values N. in the respective bins by the relevant time valueT_(MeasV), counted e.g as an amount of seconds, so as to obtain anaverage occurrence frequency value f_(C), expressed e.g. as pulses persecond for each of the amplitude bins. Since these average values arecounted as an average for the complete duration of the measuringsession, the resulting value has been found to be advantageouslyreliable. Thus, an embodiment of the condition value generator 1030operates to generate a normalized interpretable histogram. It isnormalized in the sense that since the occurrence frequency values f_(C)are averaged, the values of the normalized histogram will be useful forcomparisons with corresponding values of other normalized interpretablehistograms irrespective of the measurements session durations of themutually different histogram values. In this manner an individual valueof the normalized histogram will be useful for comparison with areference value irrespective of the measurement session durationT_(Meas) employed for generating the individual value.

According to an embodiment the condition value generator 1030 is adaptedto generate a first condition value LR_(D) in response to said sortedoutput peak values A_(PO) and said duration T_(Meas) so that

-   -   said first condition value LR_(D) is indicative of a first        amplitude value A_(LRD) having a first predetermined occurrence        rate f_(C1). According to a preferred embodiment the condition        value generator 1030 is also adapted to generate a first        condition value LR_(D) in response to said sorted output peak        values A_(PO) and said duration T_(Meas) so that said first        condition value LR_(D) is based on a selected first temporal        portion of the digital measurement signal S_(MD), S_(R).

According to an embodiment the condition value generator 1030 is alsoadapted to generate a second condition value HR_(LUB) in response tosaid sorted output peak values A_(PO) and said duration T_(Meas) so that

-   -   said second condition value HR_(LUB) is indicative of an second        amplitude value A_(HRLUB) having a second predetermined        occurrence rate f_(C2), and so that    -    said second condition value HR_(LUB) is based on said selected        first temporal portion of the digital measurement signal S_(MD),        S_(R).

According to an embodiment, the first condition value LR_(D) isindicative of the amplitude A_(LRD) of peak values A_(PO) having a firstpredetermined occurrence rate f_(C1) of e.g. f_(C1)=40 pulses persecond, and the second condition value HR_(LUB) is indicative of asecond amplitude value A_(HRLUB) having a second predeterminedoccurrence rate f_(C2) of e.g. f_(C2)=1000 pulses per second.

As mentioned above, the rectified signal S_(R) may be delivered to adigital peak value detector 310 as well as to an enveloper 250. Withreference to FIG. 12, the apparatus 14 further comprises a decimator1010 adapted to generate a decimated digital signal S_(RED) independence of said rectified signal S_(R), as illustrated in FIG. 12, sothat the decimated digital signal S_(RED) has a reduced samplingfrequency f_(SR); and

-   -   a Fourier Transformer 1020 adapted to generate a transformed        signal S_(FT) in dependence of a selected second temporal        portion of said decimated digital signal S_(RED) so that said        transformed signal S_(FT) is indicative of said vibration signal        repetition frequency f_(D).

The apparatus may be arranged to coordinate the generation of thetransformed signal S_(FT) with the generation of the first conditionvalue LR_(D) so that the selected second temporal portion of saiddecimated digital signal S_(RED) is based substantially on said selectedfirst temporal portion of the digital measurement signal S_(MD), and sothat said selected first temporal portion of the digital measurementsignal S_(MD) is generated during the variably settable durationT_(Meas) of said measuring session.

The apparatus may also comprise an associator 1035 adapted to associatethe first condition value LR_(D) with the transformed signal S_(FT), asillustrated in FIG. 12.

The FIG. 12 embodiment thus advantageously enables the delivery of afirst condition value LR_(D) which is indicative of the first amplitudevalue A_(LRD) of peak values A_(PO) having a first predeterminedoccurrence rate f_(C1) and of a transformed signal S_(FT) which isindicative of said vibration signal repetition frequency f_(D) whileensuring that the first condition value LR_(D) and the transformedsignal SFT are consistent with each other, since both of them are basedon the same or substantially the same temporal portion of the digitalmeasurement signal S_(MD). Hence, the provision of an associator 1035adapted to associate the first condition value LR_(D) with thetransformed signal S_(FT), as illustrated in FIG. 12, enablespresentation of the first condition value LR_(D) associated with thetransformed signal S_(FT). Such presentation may be achieved by thedisplay 106, as illustrated in FIG. 12. Hence, the first condition value(LR_(D)) and the transformed signal (SFT) are based on concurrentmeasurement data, or substantially the same measurement data, and assuch the first condition value (LR_(D)) and the transformed signal (SFT)may complement each other by providing mutually different perspectiveson the same event, i.e. the condition of the monitored rotatable machinepart (7,8) during the measuring session, based on data collected duringthe whole duration (T_(meas)) of the measuring session, as mentionedabove.

A sensor 450 may be provided for detecting speed of rotation f_(ROT)associated with the rotatable part 7,8 of the machine 6, as illustratedin FIGS. 1, 8 and 12, so as to generate a signal indicative of detectedspeed of rotation f_(ROT). The signal indicative of detected speed ofrotation f_(ROT) may be provided to an apparatus input 1040 forreceiving the signal indicative of detected speed of rotation f_(ROT)associated with said rotatable part 7, 8. The signal indicative ofdetected speed of rotation f_(ROT) may be delivered to the decimator1010 and/or to the condition analyzer 290 and/or to the display 106,and/or to the associator 1035, as illustrated in FIG. 12.

According to an embodiment the apparatus comprises an analyser 290having a first analyzer input 1050 for receiving said first conditionvalue LR_(D); and a second analyzer input 1060 for receiving said secondcondition value HR_(LUB); wherein the analyzer 290 is adapted togenerate a status signal indicative of whether the condition of themachine is normal or abnormal in dependence on said first conditionvalue LR_(D) and said second condition value HR_(LUB). The fact that theapparatus may generate the first condition value LR_(D) and the secondcondition value HR_(LUB) on the basis of measurement data S_(MD), S_(R)collected during the uninterrupted time period of the variably settableduration T_(Meas) of said measuring session advantageously increases thereliability of the first condition value LR_(D) and the second conditionvalue HR_(LUB) in the sense of truly reflecting the condition of themonitored part. When, for example, the monitored rotatable part is abearing in a crane which sometimes carries a heavy load, and whichsometimes runs substantially unloaded, the bearing will sometimes besubjected to a large force due to the carrying of the heavy load. Insuch a case it is desirable that the measurement data collected, i.e.the selected first temporal portion of the digital measurement signalS_(MD), S_(R), includes the time period when the bearing is subjected toa large force. The variably settable duration T_(Meas) of themeasurement session advantageously enables an operator of the apparatusto set the duration T_(Meas) so as to include the loaded time period inthe measurement session.

According to an embodiment the apparatus comprises an apparatus input1040 for receiving a signal indicative of a detected speed of rotation(f_(ROT)) associated with said rotatable part 7,8 (see FIGS. 1 and 12).The apparatus may also comprise a third analyzer input 1070 forreceiving said signal indicative of a detected speed of rotation(f_(ROT)); and a fourth analyzer input 1080 for receiving a bearingfrequency factor value (OR, IR, FTF, BS); and a fifth analyzer input1090 for receiving said transformed signal (S_(FT), f_(D)). Moreover,the analyzer may be adapted to generate a status signal indicative ofthe nature of, and/or cause for, an abnormal machine condition independence of said speed of rotation signal (f_(ROT)), said bearingfrequency factor value (OR, IR, FTF, BS) and said transformed signal(S_(FT), f_(D)).

According to an embodiment the analyzer 290, 1035 is adapted to generatea status signal indicative of a probable location of an incipient damagein dependence of

-   -   said speed of rotation signal f_(ROT),    -   said bearing frequency factor value OR, IR, FTF, BS and    -   said transformed signal S_(FT).

According to an embodiment, the analyzer 290, 1035 is adapted to extractsaid at least one vibration signal repetition frequency (f_(D)) fromsaid transformed signal (S_(FT), f_(D)); and the analyzer is adapted togenerate a frequency factor estimate (F_(fEST)) in dependence on said atleast one vibration signal repetition frequency (f_(D)) and saiddetected speed of rotation (f_(ROT)); and the analyzer is adapted tocompare the generated frequency factor estimate (F_(fEST)) with a storedplurality of frequency factors (F_(fstore1), F_(fstore2), F_(fstore3), .. . F_(fstoren)); and wherein

the analyzer is adapted to generate a status signal indicative of aprobable location of an incipient damage in dependence of said frequencyfactor comparison. This solution may advantageously provide an explicitindication to the effect that a detected damage is located e.g. on theouter ring of a monitored bearing assembly, when the generated frequencyfactor estimate (F_(fEST)) has a value that substantially corresponds toa stored value of an Outer Ring frequency factor value.

Correct detection of peak amplitude values in a sampled version of ananalogue measurement signal S_(EA) having transient vibration signalsignatures (S_(D)) having a vibration frequency (f_(SEA)) and at leastone repetition frequency (f_(D)) require a high sample rate in order toactually sample the analogue signal at a moment of peak value. Thisproblem is addressed by the following embodiment: An embodiment of anapparatus for analysing the condition of a machine having a part (7)rotatable with a speed of rotation (f_(ROT)), comprises:

an input 42 for receiving an analogue measurement signal S_(EA)indicative of a vibration signal signature (S_(D)) having a vibrationfrequency f_(SEA) and at least one repetition frequency f_(D); and anA/D converter 40, 44) adapted to generate a digital measurement signalS_(MD) dependent on the analogue measurement signal, said digitalmeasurement signal S_(MD) having a first sample rate (f_(s)), the firstsample rate being at least twice (k) said vibration frequency (f_(SEA)).

With reference to FIG. 12, this embodiment also comprises a digitalrectifier 270 adapted to perform full-wave rectification so as togenerate a rectified digital signal S_(R) dependent on said digitalmeasurement signal S_(MD); and a smoothing stage 1100 adapted togenerate a smoothened digital signal (S_(smooth)) dependent on saidrectified digital signal (S_(R)). The smoothing stage 1100 is adapted toadjust an output sample amplitude value (S_(SOUT) _(_) _(i)) upwards independence on

-   -   the amplitude of the corresponding input sample amplitude value        (S_(SIN) _(_) _(i)) and in dependence on    -   the amplitude of temporally adjacent input sample amplitude        values (S_(SIN) _(_) _(i−1), S_(SIN) _(_) _(i+1)).

Advantageously, the smoothing stage will eliminate “dents” in therectified signal, and it will do so by always adjusting the amplitudeupwards. Thus, whereas the rectified signal S_(R) may include a sampledvalue S_(SIN) _(_) _(i) having significantly lower amplitude that itstemporally adjacent neighbour samples S_(SIN) _(_) _(i−1) and S_(SIN)_(_) _(i+1), the signal S_(SMOOTH) from the smoothing stage will alwaysbe smooth. Hence, smoothing stage 1100 may be adapted to adjust anoutput sample amplitude value S_(SOUT) _(_) _(i), wherein i denotes thetemporal position of the sample, upwards in dependence on the amplitudeof the corresponding input sample amplitude value S_(SIN) _(_) _(i) andin dependence on the amplitude of temporally preceding input sampleamplitude value S_(SIN) _(_) _(i−1), as well as in dependence on theamplitude of temporally succeeding the input sample amplitude valueS_(SIN) _(_) _(i+1).

Whereas a smoothing effect may also be achieved by means of amedian-value-filter, the median-filter would also reduce the topamplitude value of the output signal in relation to the top value of therectified input signal. Hence, whereas a median-filter would make thesignal more smooth, the smoothing stage as defined above will not onlymake the signal more smooth, but it will also maintain the amplitudevalues of the highest detected amplitudes in the rectified signal.

With reference to FIG. 12, this embodiment also comprises an asymmetricdigital filter 1110 for generating an asymmetrically low pass filteredsignal S_(ASYM) in response to the smoothed digital signal S_(Smooth).The asymmetric digital filter 1110 may be adapted to generate theasymmetrically filtered signal (S_(ASYM)) so that in response to adetected positive time derivative of the smoothed digital a firstsettable filter value k is set to a first value KRise; and in responseto a detected negative time derivative of the smoothed digital signalsaid first settable filter value (k) is set to a second value kFall.

A peak detector 330 may be adapted to detect the peak value A_(P) of theasymmetrically filtered signal S_(ASYM), as illustrated in FIG. 12, andto deliver the output peak values A_(PO) on a peak value detector output315. The peak detector 330 may be adapted to limit the deliveryfrequency of said output peak values A_(PO) such that said output peakvalues A_(PO) are delivered at a maximum delivery frequency of f_(dP),wherein

f _(dP) =f _(s) /e

-   -   where f_(s) is the first sample rate of the A/D converter 40, 44        adapted to generate the digital measurement signal S_(MD), and    -   e is an a number higher than two.

According to an embodiment, the smoothing stage 1100 includes

-   -   a first peak sample selector 1100 adapted to analyze v        consecutive received sample values, and to identify the highest        amplitude of these v consecutive received sample values, and to        deliver v consecutive output sample values with at least one of        the v consecutive output sample values having an adjusted        amplitude value, said adjustment being an amplitude increase,    -   wherein, v is an integer having a value of about fs divided by        f_(SEA).

According to an embodiment, the smoothing stage includes

a first peak sample selector 1100 which is adapted to receive aplurality of temporally consecutive sample values of the rectifiedsignal S_(R); and

-   -   the first peak sample selector 1100 is adapted to identify the        amplitude of a selected sample value S_(SIN) _(_) _(i) from        among said received plurality of consecutive sample values; and    -   the first peak sample selector 1100 is adapted to analyze        -   the amplitude of the selected sample value S_(SIN) _(_)            _(i),        -   the amplitude of the sample S_(SIN) _(_) _(i−1) immediately            preceding the selected sample value S_(SIN) _(_) _(i) and        -   the amplitude of the sample S_(SIN) _(_) _(i+1) succeeding            the selected sample value S_(SIN) _(—i) ; and    -   deliver an output sample value S_(OUT) _(_) _(i) in response to        said selected sample value S_(SIN) _(_) _(i) so that said output        sample value S_(SOUT) _(_) _(i) has an amplitude corresponding        to the highest amplitude detected in said analysis.

According to an embodiment, the asymmetric digital filter 1110 isadapted to generate the asymmetrically filtered signal (S_(ASYM)) sothat

-   -   in response to a detected positive time derivative of the        smoothed digital signal (S_(Smooth)) the asymmetrically filtered        signal (S_(ASYM)) will have a positive time derivative        substantially equal to that of the smoothed digital signal        (S_(Smooth)); and    -   in response to a detected negative time derivative of the        smoothed digital signal (S_(Smooth)) the asymmetrically filtered        signal (S_(ASYM)) will have a comparatively slow response.

1. (canceled)
 2. A system for detecting an operating condition of amachine including a bearing associated with a shaft that rotates at aspeed of rotation, the system comprising: a vibration sensor configuredto detect mechanical vibrations responsive to the rotation of the shaftwith respect to the bearing; an analog to digital converter configuredto generate a digital measurement signal having sample values responsiveto the detected mechanical vibrations so that said digital measurementsignal includes a vibration signal signature; and one or more hardwareprocessors configured to: generate an output value based on at least oneof said sample values selected from a first temporal portion of thedigital measurement signal; generate a transformed signal based on asecond temporal portion of said digital measurement signal; said one ormore hardware processors being further configured to: coordinate thegeneration of said transformed signal with the generation of the outputvalue so that the second temporal portion is based on said firsttemporal portion of the digital measurement signal.
 3. The systemaccording to claim 2, including a first hardware processor location (4),a second hardware processor location (31; 28), said second hardwareprocessor location (31; 28) being separated from said first hardwareprocessor location (4) by a geographic distance, and a communicationsnetwork, wherein said one or more hardware processors include a firsthardware processor at said first hardware processor location, and asecond hardware processor at said second hardware processor location,and wherein said vibration sensor and said analog to digital converterare located at said first hardware processor location; and wherein saidfirst hardware processor has a first communications port for dataexchange via said communications network, and wherein said secondhardware processor is located at said second hardware processorlocation, said second hardware processor having a second communicationsport for data exchange via said communications network.
 4. The systemaccording to claim 3, wherein said first hardware processor isconfigured to communicate with said second hardware processor via saidcommunications network, said first hardware processor being configuredto deliver measurement data being partly processed so as to allowfurther signal processing and/or analysis to be performed at the secondlocation by said second hardware processor.
 5. The system according toclaim 2, wherein said one or more hardware processors being furtherconfigured to: generate an enveloped digital measurement signal based onsaid second temporal portion of said digital measurement signal; and togenerate said transformed signal based on said enveloped digitalmeasurement signal.
 6. The system according to claim 2, wherein said oneor more hardware processors being further configured to: generate anenveloped digital measurement signal based on said second temporalportion of said digital measurement signal; and to generate a decimatedenveloped digital measurement signal based on said enveloped digitalmeasurement signal; and to generate said transformed signal based onsaid decimated enveloped digital measurement signal.
 7. The systemaccording to claim 2, wherein said one or more hardware processors areconfigured to output an indication of said operating condition based onsaid output value and said transformed signal.
 8. The system accordingto claim 2, further comprising a user output interface configured todisplay an indication of said operating condition based on said outputvalue and said transformed signal.
 9. The system according to claim 2,wherein said output value and said transformed signal provide mutuallydifferent perspectives on the same event.
 10. The system according toclaim 2, wherein said vibration signal signature has at least onevibration signal repetition frequency and at least one vibration signalamplitude, and wherein said transformed signal is indicative of said atleast one vibration signal repetition frequency.
 11. The systemaccording to claim 2, wherein said one or more hardware processors areconfigured to extract a value from said transformed signal.
 12. Thesystem according to claim 2, wherein said one or more hardwareprocessors being configured to extract at least one vibration signalrepetition frequency value from said transformed signal.
 13. The systemaccording to claim 2, wherein at least one of said one of said one ormore hardware processors is embodied by a Digital Signal Processor. 14.The system according to claim 2, wherein said output value is anamplitude value.
 15. The system according to claim 2, wherein saidoutput value is a peak amplitude value.
 16. The system according toclaim 2, wherein said one or more hardware processors being configuredto perform trending based on a current peak amplitude value andhistorical peak amplitude values retrieved from a memory.
 17. The systemaccording to claim 2, wherein said transformed signal is a Fouriertransform.
 18. The system according to claim 2, wherein said transformedsignal is a fast Fourier transform.
 19. The system according to claim 2,wherein said vibration signal signature has at least one vibrationsignal repetition frequency and at least one vibration signal amplitude;and wherein said one or more hardware processors being furtherconfigured to: generate an enveloped digital measurement signal based onsaid second temporal portion of said digital measurement signal; and togenerate said transformed signal based on said enveloped digitalmeasurement signal, said transformed signal being a fast Fouriertransform, and wherein said one or more hardware processors areconfigured to extract at least one vibration signal repetition frequencyvalue from said transformed signal, and wherein said output value is apeak amplitude value, said peak amplitude value being based on said atleast one vibration signal amplitude.
 20. The system according to claim19, including a first hardware processor location (4), a second hardwareprocessor location (31; 28), and a communications network, wherein saidone or more hardware processors include a first hardware processor atsaid first hardware processor location, and a second hardware processorat said second hardware processor location, and wherein said vibrationsensor and said analog to digital converter are located at said firsthardware processor location; and wherein said first hardware processorhas a first communications port for data exchange via saidcommunications network, and wherein said second hardware processor islocated at said second hardware processor location, said second hardwareprocessor having a second communications port for data exchange via saidcommunications network, wherein said first hardware processor isconfigured to communicate with said second hardware processor via saidcommunications network, said first hardware processor being configuredto deliver measurement data being partly processed so as to allowfurther signal processing and/or analysis to be performed at the secondlocation (31; 28) by said second hardware processor.
 21. The systemaccording to claim 20, further comprising a user output interfaceconfigured to display an indication of said operating condition based onsaid peak amplitude value and said vibration signal repetition frequencyvalue.
 22. A method for detecting an operating condition of a machineincluding a bearing associated with a shaft that rotates at a speed ofrotation, the method comprising: generating, by way of a vibrationsensor applied to a measuring point on the machine, an analoguemeasurement signal responsive to mechanical vibrations emanating fromthe bearing during rotation of the shaft so that said analoguemeasurement signal includes a vibration signal signature having avibration signal repetition frequency and a vibration signal amplitude;sampling, by way of an analog to digital converter, said analoguemeasurement signal; generating, from said sampling, a digitalmeasurement signal having sample values responsive to the detectedmechanical vibrations so that said digital measurement signal includessaid vibration signal signature; generating, by way of one or morehardware processors, a peak amplitude value based on a first temporalportion of the digital measurement signal; generating, by way of saidone or more hardware processors, a Fourier transformed signal based on aselected second temporal portion of said digital measurement signal;coordinating, by way of said one or more hardware processors, thegeneration of said Fourier transformed signal with the generation ofsaid peak amplitude value so that said transformed signal and said peakamplitude value are based on the same or substantially the same temporalportion of the digital measurement signal.
 23. The method according toclaim 22, further comprising generating, by way of said one or morehardware processors, a first condition value which is indicative of saidpeak amplitude value, and generating, by way of said one or morehardware processors, an output which is indicative of said vibrationsignal repetition frequency.
 24. The method according to claim 23,further comprising delivering, by way of said one or more hardwareprocessors, said peak amplitude value and said output indicative of saidvibration signal repetition frequency to a display, and presenting, byway of said display, said at least one vibration signal repetitionfrequency value and said output indicative of said vibration signalrepetition frequency on said display.
 25. The method according to claim22, wherein said Fourier transformed signal is a fast Fourier transform,said method further comprising extracting, by way of said one or morehardware processors, at least one vibration signal repetition frequencyvalue from said fast Fourier transformed signal, said at least onevibration signal repetition frequency value being indicative of said atleast one vibration signal repetition frequency.
 26. The methodaccording to claim 23, wherein transmitting, via a communications portand a communications network, said first condition value and said outputindicative of said vibration signal repetition frequency from a firstlocation to a second location.
 27. A system for detecting an operatingcondition of a machine including a bearing associated with a shaft thatrotates at a speed of rotation, the system comprising: a vibrationsensor configured to detect mechanical vibrations responsive to therotation of the shaft with respect to the bearing; an analog to digitalconverter configured to generate a digital measurement signal havingamplitude sample values responsive to the detected mechanical vibrationsso that said digital measurement signal includes a vibration signalsignature; and one or more hardware processors configured to: generate asmoothened digital signal based on said digital measurement signal sothat an output sample amplitude value is adjusted upwards in dependenceon the amplitude of the corresponding input sample amplitude value andin dependence on the amplitudes of temporally adjacent input sampleamplitude values; generate an asymmetrically filtered signal based onthe smoothed digital signal so that a first settable filter value is setto a first value in response to a detected positive time derivative ofthe smoothened digital signal; and said first settable filter value isset to a second value in response to a detected negative time derivativeof the smoothened digital signal; detect peak values in saidasymmetrically filtered signal, and deliver output peak values based onsaid detected peak values.